The invention relates to machine tools in general, especially to grinding machines, and more particularly to improvements in means for protecting the guideways for mobile elements in machine tools.
It is customary to provide a machine tool with guards which overlap the guideways for wheelheads, saddles, tables and other mobile machine elements in order to shield such guideways from splashing coolant, lubricant and/or fragments of material which is being removed from a workpiece by one or more rotary, reciprocatory and/or otherwise movable tools. Such guards are normally disposed between the work area (e.g., the station where one or mor rotary grinding wheels remove material from a workpiece which is held between a headstock and a tailstock) on the one hand and the machine element(s) and the prime mover(s) therefor on the other hand. The guards can include bellows, tubular, trough-shaped or otherwise configurated components which are telescoped into each other, and/or otherwise configurated parts which are designed to prevent a lubricant, a coolant or particles of solid material from impinging upon and/or depositing on the guideways and/or on the prime mover or prime movers for one or more mobile machine elements.
In many presently known machine tools, the guards are attached to and are thus compelled to share the movements of the respective machine elements along their guideways. This can affect the accuracy of treatment which is carried out by such machine tools because the inertia, weight and/or other parameters can undesirably influence the movements of the respective machine element or elements and of the tool or tools which are mounted on and rotate, reciprocate and/or otherwise move with or relative to the associated machine elements. The so-called stick-slip effect is one of the phenomena which can affect the accuracy of treatment of workpieces in a grinding machine or another machine tool if the prime mover which imparts motion to a machine element is required to pull or push a guard jointly with the corresponding machine element. The reason is that the guards are normally in frictional engagement with their guides and their resistance to movement with the associated machine elements can vary within a wide range in response to abrupt acceleration or deceleration of the prime mover or prime movers. All this exerts an undue influence upon the quality of treatment of workpieces. For example, the influence of a guard which is to be pushed or pulled by the prime mover for a wheelhead in a grinding machine is quite pronounced when such machine is required to treat workpieces with a high or very high degree of accuracy, e.g., so that the tolerances cannot exceed a few thousandths of one millimeter.